Electronic devices exhibiting a specific electrical impedance that may also be tuned to various impedance values while part of an electronic circuit are very useful in a variety of applications. Traditional semiconductor fabrication techniques allow fabrication of devices exhibiting a single non-volatile impedance or, in the case of a conventional transistor, a configurable, but volatile impedance. These single impedance devices may be tuned to various impedance values using a variety of techniques such as mask modification programming, laser trimming, or programming of a non-volatile device (e.g., fuses, anti-fuses, and flash memory). Unfortunately, many of these techniques tend to be irreversible. In other words, the impedance value may be changed to a new desired stable state, but once changed, it cannot be changed back to another desired stable state. Other techniques, which may be reversible, involve logically combining a variety of fixed-value impedance devices in parallel and/or in series to arrive at the total desired impedance. To maintain large dynamic range without loss of sensitivity, a large number of impedance devices may be required in parallel and/or in series to achieve the desired impedance value. This combination of multiple impedance devices creates added complexity and may consume large amounts of area on an electronic device.
Additionally, semiconductor device fabrication is becoming increasingly complex and difficult as attempts are made to reduce device size to the nanometer technology range. A new fabrication and device formation plan involving relatively loose tolerances and self-assembly of sub-elements may be required to fully achieve the goal of useable electronic circuits incorporating nanometer-scale devices.
Recent research and development in the fields of nanoelectronics and molecular electronics has included several reports of molecular electronic devices comprised of two electrodes with a molecular compound disposed between the two electrodes. These reported devices have the characteristics of non-volatile configurable switches, wherein a bias may be applied to the molecular electronic device in such a manner as to cause the device to appear substantially like an open switch (i.e. a very high resistance) or substantially like a closed switch (i.e. a very low resistance). While two discrete states may be sufficient and desirable for some memory or logic applications, this approach is limited. Other digital circuits require more than two discrete states and analog applications require a continuum of impedance variations. Two-state devices also do not facilitate impedance matching, such as for high speed signal applications.
A highly controllable non-volatile device, which exhibits a programmable impedance behavior and that may be fabricated down to nanometer dimensions, where one or more dimensions are nanometer-scale, may be valuable in a wide variety of electronic applications. Further, a device that is reconfigurable throughout a range of impedance values may be valuable in fault tolerant systems, which are becoming increasingly important both at nanometer-scale and micron-scale applications.